Sonic flocculator and method of flocculating smoke or the like



24, 1940- H. w. ST. CLAIR 2,215,484

SONIC FLOCCULAIOR AND METHOD OF FLOCCULATING SMSKE OR THE LIKE Filed Oct. 10, 1958 Pef/ec/or 7; 2

INVENTOR BY /7 /'//a/" WStC/air ATTORNEY Patented Sept. 24, 1940 UNITED STATES PATENT OFFICE SONIC FLOCCULATOR AND METHOD OF FLOCCULATING SMOKE OR THE. LIKE his successors in ofi'ice Application October 10, 1938, Serial No. 234,323

'7 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 O. G. 757) This invention relates to the art of fiocculating aerosols and to a sonic fiocculator as well as to a method of flocculating smoke or the like.

Dispersions consisting of finely subdivided solid or liquid material suspended in'a gaseous medium, such as air, are known as aerosols. They are classified according to their respective modes of origin, nature and appearance as smoke, fume, dust, fog, mist or cloud. Aerosols resulting from combustion or from destructive distillation are commonly called smoke, while fume is usually produced by chemical action or by volatilization.

Dusts may be formed by natural or mechanical processes of disintegration and dispersion. In smoke and fume the particles may be either solid or liquid, while dust consists only of solid particles. Cloud, mist and fog are aerial systems consisting mainly of dispersed water or of some other volatile liquid. The great majority of all persistent aerial systems are smokes or fumes such as those formed by chemical processes, electrical or mechanical pulverization, volatilization or combustion. The present invention and the principle thereof apply generally to the flocculation of aerosols, and particularly to the flocculation of the persistent aerial systems which are commonly known as smokes or fumes.

A characteristic property of disperse systems is the Brownian motion or the random motion of the dispersed particles resulting from numerous collisions with the molecules of the medium. The

I displacement of a particle in air by this motion is about eight times what it would be in water as a medium. One of the most important results of Brownian motion is the continuous and spontaneous flocculation shown by most aerosols. The particles stick together when Brownian motion brings them in contact. Probably a high percentage of the collisions are effective. Ad-

herence also results from the majority of collisions between particles with various surfaces.

Some aerosols, such as quartz and limestone dusts, do not show spontaneous flocculation.

The abnormal behavior of such aerosols is attributed to a layer of adsorbed gas that prevents the colliding particles from sticking. Obviously, this continuous and spontaneous flocculation of most aerosols does not occur with sufiicient rapidity to prevent damage to adjacent property, such for example, as damage caused by smelter fumes.

It has been found that apparently any aerosol can be fiocculated in a relatively brief interval by subjecting it to the influence of high frequency sound waves. The equipment required consists primarily of a vibrator for producing the sound waves and a resonating chamber for producing the sound field. A magnetostrictive vibratormay be used for generating the sound waves. The sound field may be produced in essentially the same way as in the familiar Kundt dust-tube experiment. (Kundt, A., Poggendorfs Annalen der Physik, vol. 127, 1866, p. 497; also Rayleigh, Lord, Theory of Sound: vol. 2, 1896, 2d ed., p. 57). The resonating chamber may be a cylinder adjusted to resonance with the vibrator by means of a movable reflecting disc disposed at one end of the cylinder. When the resonating column is adjusted to resonance, the radiated and reflected waves interfere in such a way as to produce a standing Wave pattern of nodes and antinodes. The nodes are positions of minimum and the antinodes, of maximum sound amplitude of vibration.

When an aerosol of ammonium chloride, for example, is confined in the resonating chamber and subjected to the influence of the sound field, flocculation occurs. As soon as the sound field is set up, the aerosol begins to fiocculate and usually first appears as fine flakes, plainly visible to the naked eye. After a brief turbulent motion, these flakes collect at the antinodal positions and form large curtain-like fiocs. As these flocs become large, they settle to the bottom, and finally the fume becomes completely fiocculated. Most of the fiocculated material settles to the bottom of the chamber, but some of it may remain suspended at the antinodal positions.

In flocculating an aerosol in this manner it is advantageous to be able to pass the aerosol through the resonating or flocculating chamber in a continuous stream. This procedure may result in a considerable loss of sound energy through the inlet and outlet ports. The purposes of this invention are to provide a method of as well as a means for passing an aerosol through the flocculating chamber of a sonic fiocculator in a continuous stream without afthe same time allowing an appreciable loss either in efiiciency of the sound generating apparatus, or in sound energy through the inlet and outlet ports of the flocculating chamber.

The features of the invention are illustrated in the accompanying drawing wherein:

Fig. 1 is a diagrammatic sectional view illustrating a sonic fiocculator comprising a cylindrical flocculating chamber having a vibrator at one end and a reflector at the other;

Fig. 2 is a View illustrating the pressure amplitude along the fiocculating chambers shown in Figs. 1 and 3; and

Fig. 3 is a diagrammatic sectional view of a sonic flocculator in accordance with this invention.

A simple sonic flocculator is illustrated in Fig. 1, as comprising. a cylindrical fiocculating chamber ID with a vibrator II at one end thereof and a reflector l2 at the opposite end. When a device, of this kind is used for fiocculating an aerosol, the reflector I2 is adjusted toward or from. the vibrator to a. position at which standing waves are produced when sound waves are generated by the vibrator at the desired frequency which should be high, that is approximately 4000 cycles per second or greater. For some aerosols, such as tobacco smoke, where the particle size is very small, the minimum effective frequency is near 7000 cycles per second. Frequencies of this order may be readily obtained with magnetostrictive vibrators, as is well understood in this art. When an aerosol is introduced into the chamber [0 and a sound field of high frequency standing waves is established in this chamber, flocculation takes place in a brief interval. When the vibrator II has about the same cross sectional area as the fiocculating cylinder or chamber Hi, the sound waves are essentially plane, that is, they have a substantially planar front, and there is a loop or antinode in the standing wave system at one quarter of a wave length from the reflector l2. Other loops or antinodes are located at intervals of one half wave length. The distance from the vibrator l I to the nearest loop is slightly less than or slightly greater than one quarter of a Wave length, the deviation being determined by the ratio of the amplitude of the vibrator II to the amplitude of the gas at the loops. When the waves in the fiocculating chamber do not have a planar front, lateral vibrations are possible and when this occurs the loops are greater than one half wave length apart. The location of the loops can be calculated, knowing the dimensions of the fiocculating chamber and the wave length, but it is usually simpler to locate the loops experimentally. It will be evident, therefore, that it is advantageous to provide a vibrator having about the same cross sectional area as the flocculating chamber. When this is done, the resonating column substantially fills the fiocculating chamber and vibrations of suflicient intensity to produce flocculation throughout the chamber are assured without resorting to the expedient of unduly increasing the frequency to provide adequate intensity in some areas and greater intensity than is required in others.

If the aerosol is supplied to or gaseous media is passed from the fiocculating chamber through openings in the side walls thereof, considerable sound energy may be lost through such openings. If the waves generated by the vibrator II, for example, are plane sinusoidal waves, the pressure amplitude at any point along the fiocculating chamber may be represented by the curve in Fig. 2. The nodes of the standing wave system are at the points A, C, E and G, and the loops or antinodes are at the points B, D, F and H.

The sound energy escaping through a hole in the wall of the fiocculating chamber is proportional to the square of the pressure amplitude; consequently the location of the inlet and outlet ports in the walls of the fiocculating cylinder is very important. A minimum amount of energy will be radiated through the holes if they are located at the loops, or points B, D, F and H. The ratio of energy radiated through a hole at B to that which would be radiated by the same hole located at 0, hole, a, is small For a frequency of 13.5 kilocycles, the wave length is about 1 inch. For a hole having a diameter of inch (0: inch) or the loss of sound through a hole with its center at C is about 100 times what it would be at B.

An important feature of this invention is the location of the inlet and outlet ports at the loops of the standing wave system, at points where the axis of the hole is normal todirection of vibration of the gas. This fundamental principle is embodied in the sonic flocculator shown in Fig. 3. This sonic flocculator comprises a vertically disposed, substantially cylindrical fiocculating chamber I5 having a suitable vibrator H5 at its lower end and a reflector I1 at its upper end. At the lower end of the fiocculating chamber, the planes of the loops or antinodes of the standing wave system are indicated by the dotted lines 3 and I9 and the inlet ports 20 are disposed in rings about the fiocculating chamber at the planes of these loops. Preferably, an annular chamber 2| is disposed about the inlet ports 20 and provided with an inlet port 22. Similarly, at the upper end of this fiocculating chamber, the planes of loops of the standing wave system are indicated by the dotted lines 23 and 24 and the outlet ports 25 are disposed about the fiocculating chamber in rings located at these positions. Preferably, an annular chamber 26 is disposed about the outlet ports 25 and provided with a discharge port 21.

In using this flocculator a suitable sound field, comprising a high frequency standing wave system is established in the fiocculating chamber l5, and an aerosol may be passed continuously through the port 22 into the annular chamber 2| from which it passes through the inlet ports 20 and upwardly through the fiocculating chamber. The influence of the sound field produces fiocculation in a brief interval and the gases and some flocculated particles escape through the outlet ports 25 into the annular chamber 26 from which they are discharged through the port 21. Thus, the flocculation of an aerosol may be carried on continuously with assurance that only a negligible amount of sound energy will be lost through the ports of the fiocculating chamber.

While the invention has been illustrated as embodied in a flocculator having a. cylindrical fiocculating chamber, the principal of the invention is applicable to resonant chambers of any shape. If the flocculation chamber is not substantially cylindrical, the pattern of the loops is more complicated and the proper points to locate the inlet and outlet ports may be more difficult to determine.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

The invention described herein, if patented, may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

What I claim is:

1. A sonic fiocculator of the class described, comprising means for establishing a sound field, comprising a high frequency standing wave tem, and a chamber wave system of said sound field. 4. A sonic fiocculator of the provide for passage of an aerosol in a steady stream and remain substantially impervious to sound energy from said standing wave system,

7. The method of the class described, which comprises establishing a high frequency resonating column in an aerosol, conserving sound the resonating column in a HILLARY W. ST. CLAIR. 

